A mooring system for vessels intended to be moored offshore is a large, expensive set of equipment comprising several thousand feet of mooring line comprising chains and wire lines, a windlass or winch with redundant braking systems for deploying, tensioning and retrieving the mooring line, fairleads for directing the mooring lines, line swivels to prevent kinks in the mooring chains, anchors (or alternatively a mooring piling) for providing holding power to keep the vessel moored on station, as well as a variety of specialized equipment to satisfy various mooring conditions. For each mooring point of a vessel, separate mooring tackle is required. The mooring line of each mooring tackle will be attached to an anchor, or, in some circumstances, to a piling driven into the bottom. Turreted vessels which are expected to remain on station for extended periods of time, may have from six to sixteen mooring points.
Mooring systems are designed to industry standards to ensure that the mooring systems provide the holding power required to withstand expected weather and sea conditions. Typically, mobile offshore vessels, such as drill ships and semi submersibles engaged in drilling operations, are designed to withstand maximum weather conditions expected during a 5-10 year period within their areas of expected operation. On the other hand, floating production vessels of similar size and type are designed for maximum weather conditions expected during a 50-100 year period in their area of intended operation. Consequently, floating production vessels are designed with two to three times the mooring strength of drilling vessels.
Increased attention to personnel safety and environmental protection is creating a trend toward requiring increased mooring strengths for mooring systems, particularly for vessels in offshore oil and gas drilling service. Additionally, with current economic conditions, operators often wish to employ drilling vessels, in areas having more severe weather conditions than conditions for which the vessel mooring systems were initially designed. Also, operators are finding it economically attractive to convert existing drilling vessels into production vessels which require much stronger mooring systems. In each of these circumstances means must be found for increasing the strength of the existing vessel mooring systems, or the existing mooring systems must be replaced with stronger mooring systems. Replacement of existing vessel mooring systems is doubly expensive. Not only must the new, stronger mooring systems be procured and installed, the existing mooring systems must be removed and scrapped.
Each mooring system for large vessels may cost in the millions of dollars. For vessels having eight or more mooring systems, mooring system may cost in the tens of millions of dollars.